Digital processing of video data has greatly progressed in recent years. In particular, various systems for recording digital video data on a magnetic video cassette recorder (VCR) have progressed. FIGS. 1(a) and 1(b) are diagrams for explaining relations of the locations on a screen and the locations on the recording tracks of a recording medium in VCRs. FIG. 1(a) illustrates the locations on the screen and FIG. 1(b) illustrates the locations on the recording tracks.
FIG. 1(a) shows one frame of picture vertically divided into eight sections. FIG. 1(b) illustrates the recorded locations of the first through ninth tracks similarly divided into eight tracks. Video data are sequentially recorded on a recording medium starting from the lowest line A of the first track to its top line I. For instance, when recording one frame data on one track, data displayed in a horizontal section defined by lines a and b on a screen are recorded on a longitudinal section defined by lines A and B on a recording medium, and thereafter, in the similar manner, data displayed in horizontal sections defined by lines b through i on the screen are sequentially recorded on longitudinal sections defined by lines B through I on the recording medium. Further, for instance, when recording one frame data on two tracks, data in the horizontal section defined by the lines a and e on the screen are recorded on the longitudinal section defined by the lines A and I of the first track #1 while data in the horizontal section defined by the lines e and I on the screen are recorded on the longitudinal section defined by the lines E and I of the second track #2.
FIGS. 2(a)-2(d) are explanatory diagrams showing the relationship between trace patterns and playback signal envelopes at a triple-speed playback mode. FIG. 2(a) shows trace patterns at the triple-speed playback mode with a tracing period shown at the axis of abscissas and track pitch or tape traveling distance at the axis of ordinates. The signs "+" and "-" in the diagram represent the regular azimuths of the playback head, respectively. Further, numerals in the diagram show track numbers; odd number tracks are in the plus azimuth and even number tracks are in the minus azimuth. FIGS. 2(b) through 2(d) illustrate the signal envelope played back by the regular head, the playback output envelope by the special head and the synthetic playback output envelope by the special head and the synthetic playback output envelope obtained by both heads. FIG. 3 is an explanatory diagram showing the construction of the recording/playback heads.
Assuming that a rotary cylinder 3, as shown in FIG. 3, is used in the data recording and playback operations. The rotary cylinder 3 is provided with a pair of regular heads 1 which have mutually different azimuths and a pair of special heads 2 which have mutually different azimuths, and the azimuths of each regular head 1 and its adjacent special head 2 also differ from each other. As shown by the sign "+" in FIG. 2(a), the first track and the third track are traced by the regular head 1 of the plus azimuth in the initial tracing period, and the fourth track and the sixth track are traced by the regular head 1 of the minus azimuth in the next tracing period. Thus, the playback signal envelope shown in FIG. 2(b) is obtained by the regular head 1. Further, the second track is traced by the special head 2 in the initial tracing period and the playback signal envelope shown in FIG. 2(c) is obtained in the same manner. By combining the playback output from the regular head 1 with the playback output from the special head 2, the synthetic playback output envelope shown in FIG. 2(d) is obtained.
Table 1 shown below represents relations among the playback outputs at the triple-speed playback mode (FIG. 2(d)), the tracing locations and the locations on the screen.
TABLE 1 ______________________________________ Playback 1 Frame/1 Track 1 Frame/2 Tracks Track Track Frame Track Frame ______________________________________ 1 #1 1.sup.st Frame #1 1.sup.st Frame (A)-(C) (a)-(c) (A)-(C) (a)-(c) 2 #2 2.sup.nd Frame #2 1.sup.st Frame (C)-(G) (c)-(g) (C)-(G) (f)-(h) 3 #3 3.sup.rd Frame #3 2.sup.nd Frame (G)-(I) (g)-(i) (G)-(I) (d)-(e) 4 #4 4.sup.th Frame #4 2.sup.nd Frame (A)-(C) (a)-(c) (A)-(C) (e)-(f) 5 #5 5.sup.th Frame #5 3.sup.rd Frame (C)-(G) (c)-(g) (C)-(G) (b)-(d) 6 #6 6.sup.th Frame #6 3.sup.rd Frame (G)-(I) (g)-(i) (G)-(I) (h)-(i) 7 #7 7.sup.th Frame #7 4.sup.th Frame (A)-(C) (a)-(g) (A)-(C) (a)-(b) 8 #8 8.sup.th Frame #8 4.sup.th Frame (C)-(G) (c)-(g) (C)-(G) (f)-(h) 9 #9 9.sup.th Frame #9 5.sup.th Frame (G)-(I) (g)-(i) (G)-(I) (a)-(b) ______________________________________
As shown in FIG. 2(d) and Table 1, data A through C on the first track #1 are reproduced by the regular head 1 in the first 1/4 time interval in the initial tracing period, data of C through G on the second track #2 are reproduced by the special head 2 in the next 1/2 time, and data of G through I on the third track are reproduced by the regular head 1 on the next 1/4 time. Thereafter, data on three tracks are reproduced in the similar manner in one tracing period.
When one frame of video data are recorded on one track, the locations of A through C on the first track #1 correspond to the locations a through c on the first frame of image, the locations C through G on the second track #2 correspond to the locations c through g on the second frame of the image, and the locations G through I on the third track #3 correspond to the locations g through i on the third frame of the image, as shown in Table 1. Therefore, at the triple-speed playback mode, the picture patterns at the locations on the first through the third frames are combined and displayed as a playback picture, as shown in FIG. 4(a).
Further, when one frame of video data are recorded on two tracks, the locations A through C on the first track #1 correspond to the locations a and b on the first frame, the locations C through G on the second track #2 correspond to the locations f through h on the first frame, and the locations G through I on the third track #3 correspond to the locations d through e on the second frame as shown in Table 1. Further, the locations A through C on the fourth track #4 correspond to the locations e and f on the second frame, the locations C through G on the fifth track #5 correspond to the locations b through d on the third frame, and the locations G through I on the sixth track #6 correspond to the locations h through i on the third frame. In this case, therefore, the picture patterns at the locations on the first through the third frames are presented in mix on the playback picture, as shown in FIG. 4(b).
By the way, various proposals have been proposed in recent years for the standardization of high efficient encoding for compressing video data. The high efficient encoding technique is to encode video data at an even lower bit rate for improving efficiency of digital transmission and recording. For instance, the CCITT (Comite Consultatif International Telegraphique et Telephonique or International Telegraph and Telephone Consultative Committee) has issued a recommendation for video-conference/video-telephone standardization H.261. According to the CCITT H.261 recommendation, the encoding is made by using the frame I processed at intra-frame compression and the frame P processed an inter-frame compression (or a predictive frame compression).
FIG. 5 is a diagram for explaining the video data compression according to the CCITT recommendation.
The frame I processed intra-frame compression is the one frame of video data encoded by the DCT (Discrete Cosine Transformation) process. The inter-frame compression processed frame P is the video data encoded by the predictive encoding method using the intra-frame compression processed frame P. In addition, a greater reduction of bit rate has been made by encoding these encoded data to the data encoded in variable length code data. As the intra-frame compression processed frame I was encoded by the intra-frame information only, it is possible to decode the intra-frame compression processed frame I by a single encoded data only. On the other hand, however, the inter-frame compression processed frame P was encoded using correlations to other video data, thus the inter-frame compression processed frame P being impossible to decode by a single encoded data only.
FIG. 6 is a block diagram showing the recording section of a conventional recording/playback apparatus for variable length code using such the predictive encoding.
The luminance signal Y and the color difference signals Cr and Cb are applied to a multiplexer 11. where they are multiplexed in block of 8 pixels.times.8 horizontal tracing lines. Sampling rate of the color difference signals Cr and Cb in the horizontal direction is a half (1/2) of the luminance signal Y. Therefore, in the period when two 8.times.8 luminance locks are sampled, one 8.times.8 block of the color difference signals Cr and Cb is sampled. As shown in FIG. 7, two luminance signal blocks Y and each of the color difference signal blocks Cr and Cb total, thus four blocks in total forms a macro block. Here, two luminance signal blocks Y and each of the color difference blocks Cr and Cb represent the same location of the picture frame. The output of the multiplexer 11 is applied to a DCT circuit 13 through a subtractor 12.
When performing the intra-frame compression, a switch 14 is kept OFF and the output of the multiplexer 11 is input directly to the DCT circuit 13 as described later. A signal composed of 8.times.8 pixels per block is applied to the DCT circuit 13. The DCT circuit 13 converts the input signal into frequency components by the 8.times.8 two dimensional DCT (Digital Cosine Transformation) process. This makes it possible to reduce the spatial correlative components. The output of the DCT circuit 13 is applied to a quantizer 15 which lowers one block signal redundancy by requantizing the DCT output using a fixed quantization coefficient. Further, block pulses are supplied to the multiplexer 11, the DCT circuit 13, the quantizer 15, etc. which operate in unit of block.
The quantized data from the quantizer 15 is applied to a variable length encoder 16 and is, for instance encoded to the Huffman codes based on the result calculated from the statistical encoding quantity of the quantized output. As a result, a short time sequence of bits is assigned to data having a high appearance probability and a long time sequence of bits to data having a low appearance probability and thus, transmission quantity is further reduced. The output of the variable length encoder 16 is applied to an error correction encoder 17, which provides the output from the variable length encoder 16 with an error correction parity added to a multiplexer 19.
The output of the variable length encoder 16 is also applied to an encoding controller 18. The amount of the output data varies largely depending on input picture. So, the encoding controller 18 monitors the amount of the output data from the variable length encoder 16 and regulates the amount of the output data by controlling the quantization coefficient of the quantizer 15. Further, the encoding controller 18 may restrict the amount of the output data by controlling the variable length encoder 16.
On the other hand, a sync/ID generator 20 generates frame a sync signal and ID signal showing data contents and additional information and provides them to the multiplexer 19. The multiplexer 19 forms one sync block data with a sync signal, an ID signal, a compressed signal data and a parity and provides these data to a recording encoder (not shown). The recording encoder, after recording/encoding the output from the multiplexer 19 according to characteristic of a recording medium, records the encoded data on a recording medium (not shown).
On the other hand, if the switch 14 is ON, the current frame signal from the multiplexer 11 is subtracted from the motion compensated preceding frame, data which will be described later, in the subtractor 12 and applied to the DCT circuit 13. That is, in this case the inter-frame encoding is carried out to encode differential data using a redundancy of the inter-frame picture. When a difference between the preceding frame and the current frame is simply obtained in the inter-frame encoding, it will become large if there is any motion in the picture. So, the difference is made small by compensating the motion by obtaining a difference at the pixel location corresponding to the motion vector while detecting the motion vector by obtaining the location of the preceding frame corresponding to the prescribed location of the current frame.
That is, the output of the quantizer 15 is also applied to an inverse quantizer 21. This quantized output is inverse-quantized in the inverse quantizer 21 and further, inverse DCT processed in an inverse DCT circuit 22 and restored to the original video signal. Further, the original information cannot be played back completely in the DCT processing, requantization, inverse quantization and inverse DCT processing and part of the information lacks. In this case, as the output of the subtractor 21 is a differential information, the output of the inverse DCT circuit 22 is also a differential information. The output of the inverse DCT circuit 22 is applied to an adder 23. This output from the adder 23 is fed back through a variable delay circuit 24 which delays signals by about one frame period and a motion compensator 25, and the adder 23 reproduces the current frame data by adding differential data to the preceding frame data and provides them to the variable delay circuit 24.
The preceding frame data from the variable delay circuit 24 and the current frame data from the multiplexer 11 are applied to a motion detector 26 where motion vector is detected. The motion detector 26 obtains motion vector through a full search motion, detection by, for instance, a matching calculation. In the full search type motion detection, the current frame is divided into the prescribed number of bocks and the search range of, for instance, 15 horizontal pixels.times.8 vertical pixels are set for each block. In the search range corresponding to the preceding frame, the matching calculation is carried out for each block and an inter-pattern approximation is calculated. Then, by calculating the preceding frame block which provides the minimum distortion in the search range, the vector which is obtained by this block and the current frame block is detected as the motion vector. The motion detector 26 provides the motion vector thus obtained to the motion compensator 25.
The motion compensator 25 extracts a corresponding block data from the variable delay circuit 24, compensates it according to the motion vector and provides it to the subtractor 12 through the switch 14 and also, to the adder 23 after making the time adjustment. Thus, the motion compensated preceding frame data is supplied from the motion compensator 25 to the subtractor 12 through the switch 14 and when the switch 14 is ON, the inter-frame compression mode results and if the switch 14 is OFF, the intra-frame compression mode results.
The switch 14 is turned ON/OFF based on a motion signal. That is, the motion detector 26 generates the motion signal depending on whether the motion vector size is in excess of a prescribed threshold value and outputs it to a logic circuit 27. The logic circuit 27 controls the ON/OFF of the switch 14 by the logical judgment using the motion signal and a refresh periodic signal. The refresh periodic signal is a signal showing the intra-frame compression processed frame I shown in FIG. 5. If the input of the intra-frame compression processed frame I is represented by the refresh periodic signal, the logic circuit 27 turns the switch 14 OFF irrespective of the motion signal. Further, if the motion signal represents that the motion is relatively fast and the minimum distortion by the matching calculation exceeds the threshold value, the logic circuit 27 turns the switch 14 OFF and the intra-frame encoding is carried out for each block even when the inter-frame compression processed frame P data are input. Table 2 shown below represents the ON/OFF control of the switch 14 by the logic circuit 27.
TABLE 2 ______________________________________ Intra-Frame Compression Frame I Processed Frame Switch 14 OFF ______________________________________ Frame P Motion Vector Detected Inter- Switch 14 ON Frame Compression Processed Frame Motion Vector Unknown Switch 14 OFF Inter-Frame Compression Processed Frame ______________________________________
FIG. 8 is an explanatory diagram showing the data stream of record signals which are output from the multiplexer 19.
As shown in FIG. 8, the first and the sixth frames of the input video signal are converted to intra-frames 11 and 16, respectively, while the second through the fifth frames are converted to inter-frame compression processed frames P2 through P5. The ratio of data quantity between the intra-frame compression processed frame I and the inter-frame compression processed frame P is (3-10): 1. The amount of data of the intra-frame compression processed frame I is relatively large, while the amount of data of the inter-frame compression processed frame P is extremely reduced. Further, the data of the inter-frame compression processed frame P cannot be decoded unless other frame data are decoded.
FIG. 9 is a block diagram illustrating the decoding section (playback section) of a conventional variable length code recording/playback apparatus.
Compressed encoded data recorded on a recording medium is played back by the playback head (not shown) and then input into an error correction decoder 31. The error correction decoder 31 corrects errors produced in a data transmission and a data recording. The playback data from the error correction decoder 31 are applied to a variable length data decoder 33 through a code buffer memory 32 and decoded to prescribed length data. Further, the code buffer memory 32 may be omitted.
The output from the variable length decoder 33 is processed an inverse-quantization in an inverse quantizer 34, and then decoded by an inverse-DCT operation in an inverse DCT circuit 35. The decoded data is then applied to the terminal a of a switch 36. On the other hand, the output of the variable length decoder 33 is also applied to a header signal extractor 37. The header signal extractor 37 retrieves a header showing whether the input data is the intra-frame compression data (intra-frame data) or the inter-frame compression data (inter-frame data) and then provides the header to the switch 36. When supplied with the header shown the intra-frame compression data, the switch 36 selects the terminal a of the switch 36 and thus outputs decoded data from the inverse DCT circuit 35.
The inter-frame compression data is obtained by adding the output from the inverse DCT circuit 35 and the preceding frame output from a predictive decoder 39 using an adder 38. That is, the output of the variable length decoder 33 is applied to a motion vector extractor 40 for obtaining a motion vector. This motion vector is applied to the predictive decoder 39. On the other hand, the decoded output from the switch 36 is delayed for one frame period by a frame memory 41. The predictive decoder 39 compensates the preceding frame decoder data from the frame memory 41 according to the motion vector and provides them to the adder 38. The adder 38 outputs a inter-frame compression data to the terminal b of the switch 36 by adding the output from the predictive decoder 39 and the output from the inverse DCT circuit 35. When the inter-frame compression data is applied, the switch 36 selects the terminal b by the header an thus outputs the decoded data from the adder 38. Accordingly, the compression and expansion are carried out without delay in both of the intra-frame compression mode and the inter-frame compression mode.
However, the intra-frame compression processed frame I and the inter-frame compression processed frame P differ from each other in their encoded quantities. If the data stream shown in FIG. 8 is recorded on a recording medium, one frame is not necessarily able to playback by the playback data at the triple-speed playback mode. Further, the inter-frame compression processed frame P processed by the inter-frame compression will become not able to playback when any undecoded frame is generated as in the triple-speed playback mode, because inter-frame compression processed frame P cannot be decoded as an independent frame.
To solve the problems, the applicant of this application has proposed a method to arrange important data by concentrating them in the Japanese Patent Application (TOKU-GAN-HEI) PO2-11745. FIGS. 10(a)-10(c) are diagrams for explaining the method. FIG. 10(a) shows a trace patterns at a triple-speed playback mode and a nine-times speed playback mode. In these diagrams, the hatched sections are the areas to be played back at the triple-speed playback mode (hereinafter referred to as the specific arrange areas).
In this proposal, important data are arranged in the hatched sections shown in FIG. 10(b) at the triple-speed playback mode, while important data are arranged in the hatched sections shown in FIG. 10(c) at the ninetimes speed playback mode. These hatched sections are the areas which are played back at the triple-speed playback mode and the nine-times speed playback mode, respectively. Further, if the intra-frame data are adopted as important data, they are recorded not only in the specific arrange area but also in other section (the meshed section).
FIGS. 11(a)-11(e) are diagrams for explaining the video data.
Video data are compressed by the compression method presented by the MPEG (Moving Picture Experts Group). Further, for a video telephone/conference, 64 Kbps.times.n times rate H.261 has been presented and also the still picture compression method has been presented by the JPEG. The MPEG is for semi-moving pictures so that the transmission rate is 1.2 Mbps as adopted for CD-ROM, etc. In the MPEG, data of the first frame, the second frame, etc. shown in FIG. 11(a) are converted to the intra-frame I1, the inter-frame data B2, the inter-frame B3, the intra-frame data P4, etc. as shown in FIG. 11(b), respectively. Thus, the respective frame data are compressed at different compression rate.
Data shown in FIG. 11(b) are changed their order in order to facilitate their decoding. That is, as the inter-frame B can be decoded by decoding the inter-frame P, at a recording on a recording medium or a transmission line after changed in the order of the intra-frame II, the inter-frame P4, the inter-frame B2, the inter-frame B3, and so on.
In the normal recording, the data shown in FIG. 11(c) are sequentially recorded on a recording medium. FIG. 11(d) shows the state of this recording. On the contrary, in the method, the data arrangement is changed as shown in FIG. 11(e) to make a specific speed playback mode possible. For instance, to make the triple-speed playback mode possible, the intra-frame I data are recorded by dividing into the leading end I1(1) of the first track #1, the center I1(2) of the second track #2 and the trailing end I1(3) of the third track #3. Thus, when the hatched sections shown in FIG. 10(b) are played back, the intra-frame I data are played back.
FIGS. 12(a)-12(b) are a block diagram showing the construction of the proposed method. The same elements in FIGS. 12(a)-12(b) as those in FIG. 6 are assigned with the same reference numerals and their explanations will be omitted.
A data sequence changer 101 changes the time sequence of input signals A1, B1 and C1 and outputs signals A2, B2 and C2 to a multiplexer 102. The data of the intra-frame I and the inter-frames P and B are given as the input signals A1, B1 and C1. These frame data are composed of the luminance signal Y and color difference signals Cr and Cb, and the multiplexer 102 multiplexes the signals Y, Cr and Cb in time sequence and outputs therefrom.
The output of a variable length encoder 16 is given to an address generator 53 and a data rearranger 100 shown by the broken-line block in addition to a variable length controller 18. The data rearranger 100 is provided for recording important data (in this case, the intra-frame data) on the prescribed location on a tape shown by the oblique line in FIG. 10(a). That is, the output of the variable length encoder 16 is separated into the intra-frame data and the inter-frame data, an the inter-frame data are controlled by a memory controller 54 and stored in an inter-frame data memory 52. The address generator 53 generates address showing the correspondence of the output of a variable length encoder 26 and the frame location, and an adder 51 adds the address to the intra-frame data from the variable length encoder 16. An intra-frame data memory 57 is controlled by a memory I controller 55 and stores the output of the adder 51. Further, the adder 51 may add an address to the inter-frame data.
The memory controller 54 and the memory I controller 55 are given with encoding process information from the variable length encoder 16, respectively, and control the write into the inter-frame data memory 52 and the intra-frame data memory 57. On the other hand, when reading from the data memories 52 and 57, the data rearrangement controller 56 rearranges data to obtain a data stream, as shown in FIG. 11(e), by controlling the memory controller 54, the memory I controller 55 and a multiplexer (hereinafter referred to as MPX) 58. That is, a track number counter 103 is given with a track start signal, for instance, a head switching pulse directing the head switching, etc., and grasping the recording track number, outputs it to the data rearrangement controller 56. For instance, when corresponding to the triple-speed playback mode, the track number counter 103 outputs track numbers #1, #2 and #3 indicating three types of continuous recording tracks in time sequence repeatedly. The data rearrangement controller 56 decides an arrangement of the intra-frame data out of the data from the MPX 58 based on the output from the track number counter 103. For instance, when making the triple-speed playback mode possible, if data indicating the track #1 is given, the data rearrangement controller 56 arranges the outputs from the intra-frame data memory 57 so as to record them on the leading end of the recording track. Similarly, if data indicating the tracks #2 and #3 are given, it arranges the outputs from the intra-frame data memory 57 so as to record them at the center and the trailing end of the recording track.
Thus, the MPX 58, under the control by the data rearrangement controller 56, multiplexes the intra-frame data and outputs them to an error correction encoder 17. The error correction encoder 17 outputs the multiplexed intra-frame data with an error correction parity added to a multiplexer 19. A sync/ID generator 20 generates a sync signal and an ID signal and then output them to the multiplexer 19, which in turn outputs them by adding them to the output of the MPX 58. The output of the multiplexer 19 is recorded on a recording medium through the recording head (not shown).
On the other hand, FIGS. 13(a)-13(b) are a block diagram showing the playback section. The same elements in FIGS. 13(a) and 13(b) as those in FIG. 9 are assigned with the same reference numerals and their explanations will be omitted.
In the playback section, the same decoding operation as that in FIG. 9 is basically carried out. However, as data have been rearranged at the recording operation, the process to return the data to the original arrangement is added. That is, the playback output from a recording medium (not shown) is demodulated and the error correction is made in an error correction decoder 31 and is then given to an address and data length extractor 61 and a DMPX 62. As the intra-frame data is recorded on the prescribed location on a recording medium according to a prescribed playback speed, it is possible to reproduce the intra-frame by performing the playback at the prescribed playback speed.
The address and data length extractor 61 extracts the address and the data length of the intra-frame data. The DMPX 62 is controlled based on the data length from the address and data length extractor 61 and separating the intra-frame data and the inter-frame data, outputs them to variable length decoders 64 and 65, respectively. The variable length decoders 64 and 65 decode the input data to prescribed length data and output them to an intra-frame buffer 66 and an inter-frame buffer 67, respectively.
On the other hand, decoded data of the variable length decoders 64 and 65 are also given to a header extractor 63. The header extractor 63 is also given with the output from the address and data length extractor 61 and by generating a signal indicating to restore the time series, outputs it to a memory I controller 69, a memory controller 70 and an intra-frame data rearrangement canceller 68. The intra-frame data rearrangement canceller 68 controls the memory I controller 69, the memory controller 70 and an MPX 71 based on the indicating signal and the header information. Then, the memory I controller 69 and the memory controller 70 control the read/write of the intra-frame buffer 66 and the inter-frame buffer 67, respectively, and then output the intra-frame and the inter-frame data converted to prescribed length data of the MPX 71. The MPX 71 restores the data sequence to the original data sequence before the rearrangement operation and then outputs the data sequence to a circuit block 300 encircled with the broken line. The operation in the block 300 is the same as the process after the reverse quantization process and the decoded output is output from a switch 36. FIG. 14 is an explanatory diagram for explaining one example of data to be recorded in the specific arrangement area. Further, FIG. 15 shows the correspondence of the data with the pictures as shown in FIG. 14, and FIG. 16 shows a data stream when the data, as shown in FIG. 14, are encoded efficiently.
As shown by the hatched sections in FIG. 14, the intra-frame I is divided into five sections and these divided frame sections I1 through I5 are arranged in the prescribed area of the inter-frame P. Data I1 through I5 correspond to each one of five vertically divided sections, respectively. Now, dividing a frame into two sections vertically and five sections horizontally, the upper areas are assumed to be a(f), b(g), c(h), d(j) and e(j), the lower areas to be a'(f'), b'(g'), c'(h'), d'(I') and e'(j'), and the ten frames are assumed to be one set. Then, as shown in FIG. 15, the data I1 corresponds to the areas a and a', and the data I2 corresponds to the areas b and b'. Similarly, the data I3 through I10 correspond to the areas c, c' through j, j' on the frame, respectively.
In the first frame, the data I1 of the intra-frame I and the data P1 of the inter-frame P are arranged, while in the second frame the data I2 of the intra-frame I is arranged between the respective inter-frame P2. Similarly, in the third and the fourth frames, the data I3 and I4 of the intra-frame I are arranged between the inter-frames P3 and P4, respectively. Similarly in the fifth frame, the inter-frame P5 and the intra-frame I5 are arranged.
When these data are highly efficiently encoded, as shown in FIGS. 16(a) and 16(b), each of the frames is composed of a DC component and an AC component of the intra-frame data and the inter-frame data. Further, the data stream is rearranged so that the intra-frame data are recorded in a specific arrangement area on a recording medium
Now, when a five-times speed playback mode is made possible, a specific arrangement area will be arranged as shown by the hatched sections in FIG. 17. If one frame data is to be recorded on two tracks, the intra-frame data I1 is recorded in the specific arrangement areas of the first and the second tracks. That is, as shown in FIG. 17, the data corresponding to the areas a, a', b, b', c, c', d, d' . . . of the frame are recorded, respectively.
Therefore, at the five-times speed playback mode, the data corresponding to the frame areas a, a', b, b', c, c' . . . are played back successively and one frame is constructed by two tracings, as shown in FIG. 18(a). In the next two tracings, the data corresponding to the frame areas f, f', g, g', . . . , j, j' are played back successively to form n frames, as shown in FIG. 18(b). In the next two tracings, one frame is constructed by the data corresponding to the frame areas a, a', . . . , e, e' as shown in FIG. 18(c).
As described above, the playback section shown in FIGS. 12(a)-12(b) and 13(a)-13(b) obtains a playback picture by playing back at least intra-frame data at a specific speed playback mode. However, there was a problem in that good quality playback pictures couldn't be obtained in reverse direction playbacks. FIGS. 19(a)-19(c) and 20(a)-20(c) are explanatory diagrams for explaining the problem. FIGS. 19(a), 19(b) and 19(c) show constructions of frames played back at a double-speed playback mode, while and FIGS. 20(a), 20(b) and 20(c) show constructions of frames played back at five-times speed playback mode.
As shown in FIGS. 19(a), 19(b) and 19(c), at the double-speed playback mode the data recorded on two tracks are played back by one tracing and therefore, only one of two adjacent tracks is played back. For instance, as shown by the oblique lines in FIG. 19(a), if the data corresponding to the frame area a is first played back, the data corresponding to the area b is played back in the next tracing. Therefore, in the next five tracings only data in the areas a through e corresponding to the upper portion of the frame are played back. Further, in the next five tracings only data in the areas f through j corresponding to the upper portion of the frame are played back as shown in FIG. 19(b) and in the next five tracings only data in the areas a through e are played back, as shown in FIG. 19(c).
Further, if a reverse direction five-times speed playback mode will be executed, the tracing direction of the magnetic head is as shown by the broken line in FIG. 17 and the playback is carried out in the order reverse to that at the time of recording. For instance, when the data corresponding to the area i' is played back in the first tracing, the data corresponding to the area b is played back in the next tracing. That is, as shown by the oblique lines in FIG. 20(a), only data in the frame areas g and i' are played back in two tracings. Further, in the net two tracings, as shown in FIG. 20(b), only data corresponding to the areas d' and b are played back and in the next two tracings, as shown in FIG. 20(c), only data corresponding to the areas i' and g are played back. Thus, there was the problem in that at the playbacks other than the normal speed playback mode and the five-times speed playback mode, only part of the frame was played back and no good quality playback picture could be obtained.
Thus, conventional variable length code recording/playback apparatus, as described above had such a problem that when intra-frame data were rearranged according to a prescribed speed playback mode the picture quality at a prescribed high speed mode forward direction playback was guaranteed but no good quality specialized playback picture could be obtained in the playbacks at other speeds and in the reverse direction.